It is conventional to establish oil and gas wells in underwater fields, with the well being drilled from a vessel, platform or other operational base at the surface of the body of water. When the wells have been drilled in relatively shallow water, it has been possible to install equipment, including equipment at the wellhead, with the assistance of divers, but increasing water depths and other factors have caused prior-art workers to develop methods and apparatus which accomplish all of the necessary tasks remotely from the operational base at the surface, without depending on diver assistance.
One of the tasks involved in establishing an underwater well is the installation, operation and retrieval of well tools such as tubing hangers, casing hangers, packoff or seal devices, and the like. Other typical tasks include carrying out work-over operations, to service the well. Much work in these areas has been done and it has become common practice to install underwater well components or tools with a handling string, usually in the form of a string of drill pipe, as shown for example in U.S. Pat. No. 4,003,434, issued Jan. 18, 1977, to Garrett et al. Such methods and apparatus have also been applied to multiple string well installations, as seen for example in U.S. Pat. Nos. 3,661,206, issued May 9, 1972, to Putch et al, and 3,741,294, issued June 26, 1973, to Morrill. While such prior-art efforts have achieved considerable success in the field, there has been a continuing need both for overall improvement and for methods and apparatus which will solve a number of common problems as yet not satisfactorily met. One such problem arises first from the need to maintain communication with well pipes, typically multiple tubing strings, during such operations as landing of a tubing hanger, while providing adequately for blowout protection. That problem becomes more complicated as the water depth increases since, to provide adequate blowout protection conventionally, it is necessary that the tubing strings be positively positioned relative to the blowout preventor, and precise positioning is difficult if not impossible to achieve from the surface by prior-art practices when the strings of pipe extending from the surface to the wellhead are very long.